Systems and methods for classifying objects in digital images captured using mobile devices

ABSTRACT

In one embodiment, a method includes receiving a digital image captured by a mobile device; and using a processor of the mobile device: generating a first representation of the digital image, the first representation being characterized by a reduced resolution; generating a first feature vector based on the first representation; comparing the first feature vector to a plurality of reference feature matrices; and classifying an object depicted in the digital image as a member of a particular object class based at least in part on the comparing.

RELATED APPLICATIONS

This application is related to copending U.S. patent application Ser. No. 13/740,123, filed Jan. 11, 2013; Ser. No. 12/042,774, filed Mar. 5, 2008; and Ser. No. 12/368,685, filed Feb. 10, 2009, each of which is herein incorporated by reference in its entirety. This application is also related to U.S. Pat. No. 7,761,391, granted Jul. 20, 2010 (U.S. patent application Ser. No. 11/752,364, filed May 13, 2007) and U.S. Pat. No. 6,370,277, granted Apr. 9, 2002 (U.S. patent application Ser. No. 09/206,753, filed Dec. 7, 1998), each of which is also herein incorporated by reference in its entirety.

FIELD OF INVENTION

The present invention relates to mobile image capture and image processing, and more particularly to capturing and processing digital images using a mobile device, and classifying objects detected in such digital images.

BACKGROUND OF THE INVENTION

Digital images having depicted therein an object inclusive of documents such as a letter, a check, a bill, an invoice, etc. have conventionally been captured and processed using a scanner or multifunction peripheral coupled to a computer workstation such as a laptop or desktop computer. Methods and systems capable of performing such capture and processing are well known in the art and well adapted to the tasks for which they are employed.

However, in an era where day-to-day activities, computing, and business are increasingly performed using mobile devices, it would be greatly beneficial to provide analogous document capture and processing systems and methods for deployment and use on mobile platforms, such as smart phones, digital cameras, tablet computers, etc.

A major challenge in transitioning conventional document capture and processing techniques is the limited processing power and image resolution achievable using hardware currently available in mobile devices. These limitations present a significant challenge because it is impossible or impractical to process images captured at resolutions typically much lower than achievable by a conventional scanner. As a result, conventional scanner-based processing algorithms typically perform poorly on digital images captured using a mobile device.

In addition, the limited processing and memory available on mobile devices makes conventional image processing algorithms employed for scanners prohibitively expensive in terms of computational cost. Attempting to process a conventional scanner-based image processing algorithm takes far too much time to be a practical application on modern mobile platforms.

A still further challenge is presented by the nature of mobile capture components (e.g. cameras on mobile phones, tablets, etc.). Where conventional scanners are capable of faithfully representing the physical document in a digital image, critically maintaining aspect ratio, dimensions, and shape of the physical document in the digital image, mobile capture components are frequently incapable of producing such results.

Specifically, images of documents captured by a camera present a new line of processing issues not encountered when dealing with images captured by a scanner. This is in part due to the inherent differences in the way the document image is acquired, as well as the way the devices are constructed. The way that some scanners work is to use a transport mechanism that creates a relative movement between paper and a linear array of sensors. These sensors create pixel values of the document as it moves by, and the sequence of these captured pixel values forms an image. Accordingly, there is generally a horizontal or vertical consistency up to the noise in the sensor itself, and it is the same sensor that provides all the pixels in the line.

In contrast, cameras have many more sensors in a nonlinear array, e.g., typically arranged in a rectangle. Thus, all of these individual sensors are independent, and render image data that is not typically of horizontal or vertical consistency. In addition, cameras introduce a projective effect that is a function of the angle at which the picture is taken. For example, with a linear array like in a scanner, even if the transport of the paper is not perfectly orthogonal to the alignment of sensors and some skew is introduced, there is no projective effect like in a camera. Additionally, with camera capture, nonlinear distortions may be introduced because of the camera optics.

Conventional image processing algorithms designed to detect documents in images captured using traditional flat-bed and/or paper feed scanners may also utilize information derived from page detection to attempt to classify detected documents as members of a particular document class. However, due to the unique challenges introduced by virtue of capturing digital images using cameras of mobile devices, these conventional classification algorithms perform inadequately and are incapable of robustly classifying documents in such digital images.

Moreover, even when documents can be properly classified, the hardware limitations of current mobile devices make performing classification using the mobile device prohibitively expensive from a computational efficiency standpoint.

In view of the challenges presented above, it would be beneficial to provide an image capture and processing algorithm and applications thereof that compensate for and/or correct problems associated with image capture, processing and classification using a mobile device, while maintaining a low computational cost via efficient processing methods.

Moreover, it would be a further improvement in the field to provide object classification systems, methods and computer program products capable of robustly assigning objects to a particular class of objects and utilize information known about members of the class to further address and overcome unique challenges inherent to processing images captured using a camera of a mobile device.

SUMMARY OF THE INVENTION

In one embodiment a method includes: receiving a digital image captured by a mobile device; and using a processor of the mobile device: generating a first representation of the digital image, the first representation being characterized by a reduced resolution; generating a first feature vector based on the first representation; comparing the first feature vector to a plurality of reference feature matrices; and classifying an object depicted in the digital image as a member of a particular object class based at least in part on the comparing.

In another embodiment, a method includes: generating a first feature vector based on a digital image captured by a mobile device; comparing the first feature vector to a plurality of reference feature matrices; classifying an object depicted in the digital image as a member of a particular object class based at least in part on the comparing; and determining one or more object features of the object based at least in part on the particular object class; and performing at least one processing operation using a processor of a mobile device, the at least one processing operation selected from a group consisting of: detecting the object depicted in the digital image based at least in part on the one or more object features; rectangularizing the object depicted in the digital image based at least in part on the one or more object features; cropping the digital image based at least in part on the one or more object features; and binarizing the digital image based at least in part on the one or more object features.

In still another embodiment, a system includes a processor; and logic in and/or executable by the processor to cause the processor to: generate a first representation of a digital image captured by a mobile device; generate a first feature vector based on the first representation; compare the first feature vector to a plurality of reference feature matrices; and classify an object depicted in the digital image as a member of a particular object class based at least in part on the comparison.

In still yet another embodiment, a computer program product includes a computer readable storage medium having program code embodied therewith, the program code readable/executable by a processor to: generate a first representation of a digital image captured by a mobile device; generate a first feature vector based on the first representation; compare the first feature vector to a plurality of reference feature matrices; and classify an object depicted in the digital image as a member of a particular object class based at least in part on the comparison.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a network architecture, in accordance with one embodiment.

FIG. 2 shows a representative hardware environment that may be associated with the servers and/or clients of FIG. 1, in accordance with one embodiment.

FIG. 3A depicts a digital image of an object, according to one embodiment

FIG. 3B depicts a schematic representation of the digital image shown in FIG. 3A divided into a plurality of sections for generating a first representation of the digital image, according to one embodiment.

FIG. 3C is depicts a first representation of the digital image shown in FIG. 3A, the first representation being characterized by a reduced resolution relative to the resolution of the digital image.

FIG. 4A is a schematic representation of a plurality of subregions depicted in a digital image of a document, according to one embodiment.

FIG. 4B is a masked representation of the digital image shown in FIG. 4A, according to one embodiment.

FIG. 4C is a masked representation of the digital image shown in FIG. 4A, according to one embodiment.

FIG. 4D is a masked representation of the digital image shown in FIG. 4A, according to one embodiment.

FIG. 5 is a flowchart of a method, according to one embodiment.

FIG. 6 is a flowchart of a method, according to one embodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless otherwise specified.

The present application refers to image processing of images (e.g. pictures, figures, graphical schematics, single frames of movies, videos, films, clips, etc.) captured by cameras, especially cameras of mobile devices. As understood herein, a mobile device is any device capable of receiving data without having power supplied via a physical connection (e.g. wire, cord, cable, etc.) and capable of receiving data without a physical data connection (e.g. wire, cord, cable, etc.). Mobile devices within the scope of the present disclosures include exemplary devices such as a mobile telephone, smartphone, tablet, personal digital assistant, iPod®, iPad®, BLACKBERRY® device, etc.

However, as it will become apparent from the descriptions of various functionalities, the presently disclosed mobile image processing algorithms can be applied, sometimes with certain modifications, to images coming from scanners and multifunction peripherals (MFPs). Similarly, images processed using the presently disclosed processing algorithms may be further processed using conventional scanner processing algorithms, in some approaches.

Of course, the various embodiments set forth herein may be implemented utilizing hardware, software, or any desired combination thereof. For that matter, any type of logic may be utilized which is capable of implementing the various functionality set forth herein.

One benefit of using a mobile device is that with a data plan, image processing and information processing based on captured images can be done in a much more convenient, streamlined and integrated way than previous methods that relied on presence of a scanner. However, the use of mobile devices as document(s) capture and/or processing devices has heretofore been considered unfeasible for a variety of reasons.

In one approach, an image may be captured by a camera of a mobile device. The term “camera” should be broadly interpreted to include any type of device capable of capturing an image of a physical object external to the device, such as a piece of paper. The term “camera” does not encompass a peripheral scanner or multifunction device. Any type of camera may be used. Preferred embodiments may use cameras having a higher resolution, e.g. 8 MP or more, ideally 12 MP or more. The image may be captured in color, grayscale, black and white, or with any other known optical effect. The term “image” as referred to herein is meant to encompass any type of data corresponding to the output of the camera, including raw data, processed data, etc.

General Embodiments

In one general embodiment a method includes: receiving a digital image captured by a mobile device; and using a processor of the mobile device: generating a first representation of the digital image, the first representation being characterized by a reduced resolution; generating a first feature vector based on the first representation; comparing the first feature vector to a plurality of reference feature matrices; and classifying an object depicted in the digital image as a member of a particular object class based at least in part on the comparing.

In another general embodiment, a method includes: generating a first feature vector based on a digital image captured by a mobile device; comparing the first feature vector to a plurality of reference feature matrices; classifying an object depicted in the digital image as a member of a particular object class based at least in part on the comparing; and determining one or more object features of the object based at least in part on the particular object class; and performing at least one processing operation using a processor of a mobile device, the at least one processing operation selected from a group consisting of: detecting the object depicted in the digital image based at least in part on the one or more object features; rectangularizing the object depicted in the digital image based at least in part on the one or more object features; cropping the digital image based at least in part on the one or more object features; and binarizing the digital image based at least in part on the one or more object features.

In still another general embodiment, a system includes a processor; and logic in and/or executable by the processor to cause the processor to: generate a first representation of a digital image captured by a mobile device; generate a first feature vector based on the first representation; compare the first feature vector to a plurality of reference feature matrices; and classify an object depicted in the digital image as a member of a particular object class based at least in part on the comparison.

In still yet another general embodiment, a computer program product includes a computer readable storage medium having program code embodied therewith, the program code readable/executable by a processor to: generate a first representation of a digital image captured by a mobile device; generate a first feature vector based on the first representation; compare the first feature vector to a plurality of reference feature matrices; and classify an object depicted in the digital image as a member of a particular object class based at least in part on the comparison.

As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as “logic,” “circuit,” “module” or “system.” Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain or store a program for use by or in connection with an instruction execution system, apparatus, processor, or device.

A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband, as part of a carrier wave, an electrical connection having one or more wires, an optical fiber, etc. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.

Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

Aspects of the present invention are described below with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

FIG. 1 illustrates an architecture 100, in accordance with one embodiment. As shown in FIG. 1, a plurality of remote networks 102 are provided including a first remote network 104 and a second remote network 106. A gateway 101 may be coupled between the remote networks 102 and a proximate network 108. In the context of the present architecture 100, the networks 104, 106 may each take any form including, but not limited to a LAN, a WAN such as the Internet, public switched telephone network (PSTN), internal telephone network, etc.

In use, the gateway 101 serves as an entrance point from the remote networks 102 to the proximate network 108. As such, the gateway 101 may function as a router, which is capable of directing a given packet of data that arrives at the gateway 101, and a switch, which furnishes the actual path in and out of the gateway 101 for a given packet.

Further included is at least one data server 114 coupled to the proximate network 108, and which is accessible from the remote networks 102 via the gateway 101. It should be noted that the data server(s) 114 may include any type of computing device/groupware. Coupled to each data server 114 is a plurality of user devices 116. Such user devices 116 may include a desktop computer, lap-top computer, hand-held computer, printer or any other type of logic. It should be noted that a user device 111 may also be directly coupled to any of the networks, in one embodiment.

A peripheral 120 or series of peripherals 120, e.g., facsimile machines, printers, networked and/or local storage units or systems, etc., may be coupled to one or more of the networks 104, 106, 108. It should be noted that databases and/or additional components may be utilized with, or integrated into, any type of network element coupled to the networks 104, 106, 108. In the context of the present description, a network element may refer to any component of a network.

According to some approaches, methods and systems described herein may be implemented with and/or on virtual systems and/or systems which emulate one or more other systems, such as a UNIX system which emulates an IBM z/OS environment, a UNIX system which virtually hosts a MICROSOFT WINDOWS environment, a MICROSOFT WINDOWS system which emulates an IBM z/OS environment, etc. This virtualization and/or emulation may be enhanced through the use of VMWARE software, in some embodiments.

In more approaches, one or more networks 104, 106, 108, may represent a cluster of systems commonly referred to as a “cloud.” In cloud computing, shared resources, such as processing power, peripherals, software, data, servers, etc., are provided to any system in the cloud in an on-demand relationship, thereby allowing access and distribution of services across many computing systems. Cloud computing typically involves an Internet connection between the systems operating in the cloud, but other techniques of connecting the systems may also be used.

FIG. 2 shows a representative hardware environment associated with a user device 116 and/or server 114 of FIG. 1, in accordance with one embodiment. Such figure illustrates a typical hardware configuration of a workstation having a central processing unit 210, such as a microprocessor, and a number of other units interconnected via a system bus 212.

The workstation shown in FIG. 2 includes a Random Access Memory (RAM) 214, Read Only Memory (ROM) 216, an I/O adapter 218 for connecting peripheral devices such as disk storage units 220 to the bus 212, a user interface adapter 222 for connecting a keyboard 224, a mouse 226, a speaker 228, a microphone 232, and/or other user interface devices such as a touch screen and a digital camera (not shown) to the bus 212, communication adapter 234 for connecting the workstation to a communication network 235 (e.g., a data processing network) and a display adapter 236 for connecting the bus 212 to a display device 238.

The workstation may have resident thereon an operating system such as the Microsoft Windows® Operating System (OS), a MAC OS, a UNIX OS, etc. It will be appreciated that a preferred embodiment may also be implemented on platforms and operating systems other than those mentioned. A preferred embodiment may be written using JAVA, XML, C, and/or C++ language, or other programming languages, along with an object oriented programming methodology. Object oriented programming (OOP), which has become increasingly used to develop complex applications, may be used.

An application may be installed on the mobile device, e.g., stored in a nonvolatile memory of the device. In one approach, the application includes instructions to perform processing of an image on the mobile device. In another approach, the application includes instructions to send the image to a remote server such as a network server. In yet another approach, the application may include instructions to decide whether to perform some or all processing on the mobile device and/or send the image to the remote site.

In various embodiments, the presently disclosed methods, systems and/or computer program products may utilize and/or include any of the functionalities disclosed in related U.S. patent application Ser. No. 13/740,123, filed Jan. 11, 2013. For example, digital images suitable for processing according to the presently disclosed algorithms may be subjected to any image processing operations disclosed in the aforementioned patent application, such as page detection, rectangularization, detection of uneven illumination, illumination normalization, resolution estimation, blur detection, etc.

In more approaches, the presently disclosed methods, systems, and/or computer program products may be utilized with, implemented in, and/or include one or more user interfaces configured to facilitate performing any functionality disclosed herein and/or in the aforementioned related patent application, such as an image processing mobile application, a case management application, and/or a classification application, in multiple embodiments.

In still more approaches, the presently disclosed systems, methods and/or computer program products may be advantageously applied to one or more of the use methodologies and/or scenarios disclosed in the aforementioned related patent application, among others that would be appreciated by one having ordinary skill in the art upon reading these descriptions.

It will further be appreciated that embodiments presented herein may be provided in the form of a service deployed on behalf of a customer to offer service on demand.

Document Classification

In accordance with one inventive embodiment commensurate in scope with the present disclosures, as shown in FIG. 5, a method 500 is shown. The method 500 may be carried out in any desired environment, and may include embodiments and/or approaches described in relation to FIGS. 1-4D, among others. Of course, more or less operations than those shown in FIG. 5 may be performed in accordance method 500 as would be appreciated by one of ordinary skill in the art upon reading the present descriptions.

In operation 502, a digital image captured by a mobile device is received.

In one embodiment the digital image may be characterized by a native resolution. As understood herein, a “native resolution” may be an original, native resolution of the image as originally captured, but also may be a resolution of the digital image after performing some pre-classification processing such as any of the image processing operations described above and in copending U.S. patent application Ser. No. 13/740,123, filed Jan. 11, 2013, a virtual re-scan (VRS) processing as disclosed in related U.S. Pat. No. 6,370,277, etc. as would be understood by one having ordinary skill in the art upon reading the present descriptions. In one embodiment, the native resolution is approximately 500 pixels by 600 pixels (i.e. a 500×600 digital image) for a digital image of a driver license subjected to processing by VRS before performing classification. Moreover, the digital image may be characterized as a color image in some approaches, and in still more approaches may be a cropped-color image, i.e. a color image depicting substantially only the object to be classified, and not depicting image background.

In operation 504, a first representation of the digital image is generated using a processor of the mobile device. The first representation may be characterized by a reduced resolution, in one approach. As understood herein, a “reduced resolution” may be any resolution less than the native resolution of the digital image, and more particularly any resolution suitable for subsequent analysis of the first representation according to the principles set forth herein.

In preferred embodiments, the reduced resolution is sufficiently low to minimize processing overhead and maximize computational efficiency and robustness of performing the algorithm on the respective mobile device, host device and/or server platform. For example, in one approach the first representation is characterized by a resolution of about 25 pixels by 25 pixels, which has been experimentally determined to be a particularly efficient and robust reduced resolution for processing of relatively small documents, such as business cards, driver licenses, receipts, etc. as would be understood by one having ordinary skill in the art upon reading the present descriptions.

Of course, in other embodiments, different resolutions may be employed without departing from the scope of the present disclosure. For example, classification of larger documents or objects may benefit from utilizing a higher resolution such as 50 pixels by 50 pixels, 100 pixels by 100 pixels, etc. to better represent the larger document or object for robust classification and maximum computational efficiency. The resolution utilized may or may not have the same number of pixels in each dimension. Moreover, the most desirable resolution for classifying various objects within a broad range of object classes may be determined experimentally according to a user's preferred balance between computational efficiency and classification robustness. In still more embodiments, any resolution may be employed, and preferably the resolution is characterized by comprising between 1 pixel and about 1000 pixels in a first dimension, and between 1 and about 1000 pixels in a second dimension.

One exemplary embodiment of inputs, outputs and/or results of a process flow for generating the first representation will now be presented with particular reference to FIGS. 3A-3C, which respectively depict: a digital image before being divided into sections (e.g. digital image 300 as shown in FIG. 3A); a digital image divided into sections (e.g. sections 304 as shown in FIG. 3B); and a first representation of the digital image (e.g. representation 310 as shown in FIG. 3C) characterized by a reduced resolution.

As shown in FIGS. 3A-3B, a digital image 300 captured by a mobile device may be divided into a plurality of sections 304. Each section may comprise a plurality of pixels 306, which may comprise a substantially rectangular grid of pixels such that the section has dimensions of p_(S(x)) horizontal pixels (p_(S(x))=4 as shown in FIG. 3B) by p_(S(y)) vertical pixels (p_(S(y))=4 as shown in FIG. 3B).

In one general embodiment, a first representation may be generated by dividing a digital image R (having a resolution of x_(R) pixels by y_(R) pixels) into S_(x) horizontal sections and S_(y) vertical sections and thus may be characterized by a reduced resolution r of S_(x) pixels by S_(y) pixels. Thus, generating the first representation essentially includes generating a less-granular representation of the digital image.

For example, in one approach the digital image 300 is divided into S sections, each section 304 corresponding to one portion of an s-by-s grid 302. Generating the first representation involves generating a s-pixel-by-s-pixel first representation 310, where each pixel 312 in the first representation 310 corresponds to one of the S sections 304 of the digital image, and wherein each pixel 312 is located in a position of the first representation 310 corresponding to the location of the corresponding section 304 in the digital image, i.e. the upper-leftmost pixel 312 in the first representation corresponds to the upper-leftmost section 304 in the digital image, etc.

Of course, other reduced resolutions may be employed for the first representation, ideally but not necessarily according to limitations and/or features of a mobile device, host device, and or server platform being utilized to carry out the processing, the characteristics of the digital image (resolution, illumination, presence of blur, etc.) and/or characteristics of the object which is to be detected and/or classified (contrast with background, presence of text or other symbols, closeness of fit to a general template, etc.) as would be understood by those having ordinary skill in the art upon reading the present descriptions.

In some approaches, generating the first representation may include one or more alternative and/or additional suboperations, such as dividing the digital image into a plurality of sections. The digital image may be divided into a plurality of sections in any suitable manner, and in one embodiment the digital image is divided into a plurality of rectangular sections. Of course, sections may be characterized by any shape, and in alternative approaches the plurality of sections may or may not represent the entire digital image, may represent an oversampling of some regions of the image, or may represent a single sampling of each pixel depicted in the digital image. In a preferred embodiment, as discussed above regarding FIGS. 3A-3C, the digital image is divided into S substantially square sections 304 to form an s×s grid 302.

In further approaches, generating the first representation may also include determining, for each section of the digital image, at least one characteristic value, where each characteristic value corresponds to one or more features descriptive of the section. Within the scope of the present disclosures, any feature that may be expressed as a numerical value is suitable for use in generating the first representation, e.g. an average brightness or intensity (0-255) across each pixel in the section, an average value (0-255) of each color channel of each pixel in the section, such as an average red-channel value, and average green-channel value, and an average blue-channel value for a red-green-blue (RGB) image, etc. as would be understood by one having ordinary skill in the art upon reading the present descriptions.

With continuing reference to FIGS. 3A-3C, in some embodiments each pixel 312 of the first representation 310 corresponds to one of the S sections 304 not only with respect to positional correspondence, but also with respect to feature correspondence. For example, in one approach generating the first representation 310 may additionally include determining a characteristic section intensity value i_(S) by calculating the average of the individual intensity values i_(P) of each pixel 306 in the section 304. Then, each pixel 312 in the first representation 310 is assigned an intensity value equal to the average intensity value i_(S) calculated for the corresponding section 304 of the digital image 300. In this manner, the first representation 310 reflects a less granular, normalized representation of the features depicted in digital image 300.

Of course, the pixels 312 comprising the first representation 310 may be represented using any characteristic value or combination of characteristic values without departing from the scope of the presently disclosed classification methods. Further, characteristic values may be computed and/or determined using any suitable means, such as by random selection of a characteristic value from a distribution of values, by a statistical means or measure, such as an average value, a spread of values, a minimum value, a maximum value, a standard deviation of values, a variance of values, or by any other means that would be known to a skilled artisan upon reading the instant descriptions.

In operation 506, a first feature vector is generated based on the first representation.

The first feature vector and/or reference feature matrices may include a plurality of feature vectors, where each feature vector corresponds to a characteristic of a corresponding object class, e.g. a characteristic minimum, maximum, average, etc. brightness in one or more color channels at a particular location (pixel or section), presence of a particular symbol or other reference object at a particular location, dimensions, aspect ratio, pixel density (especially black pixel density, but also pixel density of any other color channel), etc.

As would be understood by one having ordinary skill in the art upon reading the present descriptions, feature vectors suitable for inclusion in first feature vector and/or reference feature matrices comprise any type, number and/or length of feature vectors, such as described in U.S. patent application Ser. No. 12/042,774, filed Mar. 5, 2008; and Ser. No. 12/368,685, filed Feb. 10, 2009 and/or U.S. Pat. No. 7,761,391, granted Jul. 20, 2010 (U.S. patent application Ser. No. 11/752,364, filed May 13, 2007).

In operation 508, the first feature vector is compared to a plurality of reference feature matrices.

The comparing operation 508 may be performed according to any suitable vector matrix comparison, such as described in U.S. patent application Ser. No. 12/042,774, filed Mar. 5, 2008; and Ser. No. 12/368,685, filed Feb. 10, 2009 and U.S. Pat. No. 7,761,391, granted Jul. 20, 2010 (U.S. patent application Ser. No. 11/752,364, filed May 13, 2007).

Thus, in such approaches the comparing may include an N-dimensional feature space comparison. In at least one approach, N is greater than 50, but of course, N may be any value sufficiently large to ensure robust classification of objects into a single, correct object class, which those having ordinary skill in the art reading the present descriptions will appreciate to vary according to many factors, such as the complexity of the object, the similarity or distinctness between object classes, the number of object classes, etc.

As understood herein, “objects” include any tangible thing represented in an image and which may be described according to at least one unique characteristic such as color, size, dimensions, shape, texture, or representative feature(s) as would be understood by one having ordinary skill in the art upon reading the present descriptions. Additionally, objects include or classified according to at least one unique combination of such characteristics. For example, in various embodiments objects may include but are in no way limited to persons, animals, vehicles, buildings, landmarks, documents, furniture, plants, etc. as would be understood by one having ordinary skill in the art upon reading the present descriptions.

For example, in one embodiment where attempting to classify an object depicted in a digital image as one of only a small number of object classes (e.g. 3-5 object classes), each object class being characterized by a significant number of starkly distinguishing features or feature vectors (e.g. each object class corresponding to an object or object(s) characterized by very different size, shape, color profile and/or color scheme and easily distinguishable reference symbols positioned in unique locations on each object class, etc.), a relatively low value of N may be sufficiently large to ensure robust classification.

On the other hand, where attempting to classify an object depicted in a digital image as one of a large number of object classes (e.g. 30 or more object classes), and each object class is characterized by a significant number of similar features or feature vectors, and only a few distinguishing features or feature vectors, a relatively high value of N may be preferable to ensure robust classification. Similarly, the value of N is preferably chosen or determined such that the classification is not only robust, but also computationally efficient; i.e. the classification process(es) introduce only minimal processing overhead to the device(s) or system(s) utilized to perform the classification algorithm.

The value of N that achieves the desired balance between classification robustness and processing overhead will depend on many factors such as described above and others that would be appreciated by one having ordinary skill in the art upon reading the present descriptions. Moreover, determining the appropriate value of N to achieve the desired balance may be accomplished using any known method or equivalent thereof as understood by a skilled artisan upon reading the instant disclosures.

In a concrete implementation, directed to classifying driver licenses according to state and distinguishing driver licenses from myriad other document types, it was determined that a 625-dimensional comparison (N=625) provided a preferably robust classification without introducing unsatisfactorily high overhead to processing performed using a variety of current-generation mobile devices.

In operation 510, an object depicted in the digital image is classified as a member of a particular object class based at least in part on the comparing operation 508. More specifically, the comparing operation 508 may involve evaluating each feature vector of each reference feature matrix, or alternatively evaluating a plurality of feature matrices for objects belonging to a particular object class, and identifying a hyper-plane in the N-dimensional feature space that separates the feature vectors of one reference feature matrix from the feature vectors of other reference feature matrices. In this manner, the classification algorithm defines concrete hyper-plane boundaries between object classes, and may assign an unknown object to a particular object class based on similarity of feature vectors to the particular object class and/or dissimilarity to other reference feature matrix profiles.

In the simplest example of such feature-space discrimination, imagining a two-dimensional feature space with one feature plotted along the ordinate axis and another feature plotted along the abscissa, objects belonging to one particular class may be characterized by feature vectors having a distribution of values clustered in the lower-right portion of the feature space, while another class of objects may be characterized by feature vectors exhibiting a distribution of values clustered in the upper-left portion of the feature space, and the classification algorithm may distinguish between the two by identifying a line between each cluster separating the feature space into two classes—“upper left” and “lower-right.” Of course, as the number of dimensions considered in the feature space increases, the complexity of the classification grows rapidly, but also provides significant improvements to classification robustness, as will be appreciated by one having ordinary skill in the art upon reading the present descriptions.

Additional Processing

In some approaches, classification according to embodiments of the presently disclosed methods may include one or more additional and/or alternative features and/or operations, such as described below.

In one embodiment, classification such as described above may additionally and/or alternatively include assigning a confidence value to a plurality of putative object classes based on the comparing operation (e.g. as performed in operation 508 of method 500) the presently disclosed classification methods, systems and/or computer program products may additionally and/or alternatively determine a location of the mobile device, receive location information indicating the location of the mobile device, etc. and based on the determined location, a confidence value of a classification result corresponding to a particular location may be adjusted. For example, if a mobile device is determined to be located in a particular state (e.g. Maryland) based on a GPS signal, then during classification, a confidence value may be adjusted for any object class corresponding to the particular state (e.g. Maryland Driver License, Maryland Department of Motor Vehicle Title/Registration Form, Maryland Traffic Violation Ticket, etc. as would be understood by one having ordinary skill in the art upon reading the present descriptions).

Confidence values may be adjusted in any suitable manner, such as increasing a confidence value for any object class corresponding to a particular location, decreasing a confidence value for any object class not corresponding to a particular location, normalizing confidence value(s) based on correspondence/non-correspondence to a particular location, etc. as would be understood by the skilled artisan reading the present disclosures.

The mobile device location may be determined using any known method, and employing hardware components of the mobile device or any other number of devices in communication with the mobile device, such as one or more satellites, wireless communication networks, servers, etc. as would be understood by one having ordinary skill in the art upon reading the present descriptions.

For example, the mobile device location may be determined based in whole or in part on one or more of a global-positioning system (GPS) signal, a connection to a wireless communication network, a database of known locations (e.g. a contact database, a database associated with a navigational tool such as Google Maps, etc.), a social media tool (e.g. a “check-in” feature such as provided via Facebook, Google Plus, Yelp, etc.), an IP address, etc. as would be understood by one having ordinary skill in the art upon reading the present descriptions.

In more embodiments, classification additionally and/or alternatively includes outputting an indication of the particular object class to a display of the mobile device; and receiving user input via the display of the mobile device in response to outputting the indication. While the user input may be of any known type and relate to any of the herein described features and/or operations, preferably user input relates to confirming, negating or modifying the particular object class to which the object was assigned by the classification algorithm.

The indication may be output to the display in any suitable manner, such as via a push notification, text message, display window on the display of the mobile device, email, etc. as would be understood by one having ordinary skill in the art. Moreover, the user input may take any form and be received in any known manner, such as detecting a user tapping or pressing on a portion of the mobile device display (e.g. by detecting changes in resistance, capacitance on a touch-screen device, by detecting user interaction with one or more buttons or switches of the mobile device, etc.)

In one embodiment, classification further includes determining one or more object features of a classified object based at least in part on the particular object class. Thus, classification may include determining such object features using any suitable mechanism or approach, such as receiving an object class identification code and using the object class identification code as a query and/or to perform a lookup in a database of object features organized according to object class and keyed, hashed, indexed, etc. to the object class identification code.

Object features within the scope of the present disclosures may include any feature capable of being recognized in a digital image, and preferably any feature capable of being expressed in a numerical format (whether scalar, vector, or otherwise), e.g. location of subregion containing reference object(s) (especially in one or more object orientation states, such as landscape, portrait, etc.) object color profile, or color scheme, object subregion color profile or color scheme, location of text, etc. as would be understood by one having ordinary skill in the art upon reading the present descriptions.

In accordance with another inventive embodiment commensurate in scope with the present disclosures, as shown in FIG. 6, a method 600 is shown. The method 600 may be carried out in any desired environment, and may include embodiments and/or approaches described in relation to FIGS. 1-4D, among others. Of course, more or less operations than those shown in FIG. 6 may be performed in accordance method 600 as would be appreciated by one of ordinary skill in the art upon reading the present descriptions.

In operation 602, a first feature vector is generated based on a digital image captured by a mobile device.

In operation 604, the first feature vector is compared to a plurality of reference feature matrices.

In operation 606, an object depicted in the digital image is classified as a member of a particular object class based at least in part on the comparing (e.g. the comparing performed in operation 604).

In operation 608, one or more object features of the object are determined based at least in part on the particular object class.

In operation 610, a processing operation is performed. The processing operation includes performing one or more of the following subprocesses: detecting the object depicted in the digital image based at least in part on the one or more object features; rectangularizing the object depicted in the digital image based at least in part on the one or more object features; cropping the digital image based at least in part on the one or more object features; and binarizing the digital image based at least in part on the one or more object features.

As will be further appreciated by one having ordinary skill in the art upon reading the above descriptions of document classification, in various embodiments it may be advantageous to perform one or more additional processing operations, such as the subprocesses described above with reference to operation 610, on a digital image based at least in part on object features determined via document classification.

For example, after classifying an object depicted in a digital image, such as a document, it may be possible to refine other processing parameters, functions, etc. and/or utilize information known to be true for the class of objects to which the classified object belongs, such as object shape, size, dimensions, location of regions of interest on and/or in the object, such as regions depicting one or more symbols, patterns, text, etc. as would be understood by one having ordinary skill in the art upon reading the present descriptions.

Regarding performing page detection based on classification, it may be advantageous in some approaches to utilize information known about an object belonging to a particular object class in order to improve object detection capabilities. For example, and as would be appreciated by one having ordinary skill in the art, it may be less computationally expensive, and/or may result in a higher-confidence or higher-quality result to narrow a set of characteristics that may potentially identify an object in a digital image to one or a few discrete, known characteristics, and simply search for those characteristic(s).

Exemplary characteristics that may be utilized to improve object detection may include characteristics such as object dimensions, object shape, object color, one or more reference features of the object class (such as reference symbols positioned in a known location of a document).

In another approach, object detection may be improved based on the one or more known characteristics by facilitating an object detection algorithm distinguishing regions of the digital image depicting the object from regions of the digital image depicting other objects, image background, artifacts, etc. as would be understood by one having ordinary skill in the art upon reading the present descriptions. For example, if objects belonging to a particular object class are known to exhibit a particular color profile or scheme, it may be simpler and/or more reliable to attempt detecting the particular color profile or scheme within the digital image rather than detecting a transition from one color profile or scheme (e.g. a background color profile or scheme) to another color profile or scheme (e.g. the object color profile or scheme), especially if the two colors profiles or schemes are not characterized by sharply contrasting features.

Regarding performing rectangularization based on classification, it may be advantageous in some approaches to utilize information known about an object belonging to a particular object class in order to improve object rectangularization capabilities. For example, and as would be appreciated by one having ordinary skill in the art, it may be less computationally expensive, and/or may result in a higher-confidence or higher-quality result to transform a digital representation of an object from a native appearance to a true configuration based on a set of known object characteristics that definitively represent the true object configuration, rather than attempting to estimate the true object configuration from the native appearance and project the native appearance onto an estimated object configuration.

In one approach, the classification may identify known dimensions of the object, and based on these known dimensions the digital image may be rectangularized to transform a distorted representation of the object in the digital image into an undistorted representation (e.g. by removing projective effects introduced in the process of capturing the image using a camera of a mobile device rather than a traditional flat-bed scanner, paper-feed scanner or other similar multifunction peripheral (MFP)).

Regarding performing cropping based on classification, and similar to the principles discussed above regarding rectangularization, it may be advantageous in some approaches to utilize information known about an object belonging to a particular object class to improve cropping of digital images depicting the object such that all or significantly all of the cropped image depicts the object and not image background (or other objects, artifacts, etc. depicted in the image).

As a simple example, it may be advantageous to determine an object's known size, dimensions, configuration, etc. according to the object classification and utilize this information to identify a region of the image depicting the object from regions of the image not depicting the object, and define crop lines surrounding the object to remove the regions of the image not depicting the object.

Regarding performing binarization based on classification, the presently disclosed classification algorithms provide several useful improvements to mobile image processing. Several exemplary embodiments of such improvements will now be described with reference to FIGS. 4A-4D.

For example, binarization algorithms generally transform a multi-tonal digital image (e.g. grayscale, color, or any other image such as image 400 exhibiting more than two tones) into a bitonal image, i.e. an image exhibiting only two tones (typically white and black). Those having ordinary skill in the art will appreciate that attempting to binarize a digital image depicting an object with regions exhibiting two or more distinct color profiles and/or color schemes (e.g. a region depicting a color photograph 402 as compared to a region depicting a black/white text region 404, a color-text region 406, a symbol 408 such as a reference object, watermark, etc. object background region 410, etc.) may produce an unsuccessful or unsatisfactory result.

As one explanation, these difficulties may be at least partially due to the differences between the color profiles, schemes, etc., which counter-influence a single binarization transform. Thus, providing an ability to distinguish each of these regions having disparate color schemes or profiles and define separate binarization parameters for each may greatly improve the quality of the resulting bitonal image as a whole and with particular respect to the quality of the transformation in each respective region.

According to one exemplary embodiment shown in FIGS. 4A-4B, improved binarization may include determining an object class color profile and/or scheme (e.g. determining a color profile and/or color scheme for object background region 410); adjusting one or more binarization parameters based on the object class color profile and/or color scheme; and thresholding the digital image using the one or more adjusted binarization parameters.

Binarization parameters may include any parameter of any suitable binarization process as would be appreciated by those having ordinary skill in the art reading the present descriptions, and binarization parameters may be adjusted according to any suitable methodology. For example, with respect to adjusting binarization parameters based on an object class color profile and/or color scheme, binarization parameters may be adjusted to over- and/or under-emphasize a contribution of one or more color channels, intensities, etc. in accordance with the object class color profile/scheme (such as under-emphasizing the red channel for an object class color profile/scheme relatively saturated by red hue(s), etc.).

Similarly, in other embodiments such as particularly shown in FIGS. 4B-4D, improved binarization may include determining an object class mask, applying the object class mask to the digital image and thresholding a subregion of the digital image based on the object class mask. The object class mask may be any type of mask, with the condition that the object class mask provides information regarding the location of particular regions of interest characteristic to objects belonging to the class (such as a region depicting a color photograph 402, a region depicting a black/white text region 404, a color-text region 406, a symbol region depicting a symbol 408 such as a reference object, watermark, etc., an object background region 410, etc.) and enabling the selective inclusion and/or exclusion of such regions from the binarization operation(s).

For example, as shown in FIG. 4B, improved binarization includes determining an object class mask 420 identifying regions such as discussed immediately above and applying the object class mask 420 to exclude from binarization all of the digital image 400 except a single region of interest, such as object background region 410. Alternatively the entire digital image may be masked-out and a region of interest such as object background region 410 subsequently masked-in to the binarization process. Moreover, in either event the masking functionality now described with reference to FIG. 4B may be combined with the exemplary color profile and/or color scheme information functionality described above, for example by obtaining both the object class mask and the object color profile and/or color scheme, applying the object class mask to exclude all of the digital image from binarization except object background region 410, adjusting one or more binarization parameters based on the object background region color profile and/or color scheme, and thresholding the object background region 410 using the adjusted binarization parameters.

Extending the principle shown in FIG. 4B, multiple regions of interest may be masked-in and/or masked-out using object class mask 420 to selectively designate regions and/or parameters for binarization in a layered approach designed to produce high-quality bitonal images. For example, as shown in FIG. 4C multiple text regions 404, 406 may be retained for binarization (potentially using adjusted parameters) after applying object class mask 420, for example to exclude all non-text regions from binarization, in some approaches.

Similarly, it may be advantageous to simply exclude only a portion of an image from binarization, whether or not adjusting any parameters. For example, with reference to FIG. 4D, it may be desirable to mask-out a unique region of a digital image 400, such as a region depicting a color photograph 402, using an object class mask 420. Then, particularly in approaches where the remaining portion of the digital image 400 is characterized by a single color profile and/or color scheme, or a small number (i.e. no more than 3) substantially similar color profile and/or color schemes, binarization may be performed to clarify the remaining portions of the digital image 400. Subsequently, the masked-out unique region may optionally be restored to the digital image 400, with the result being an improved bitonal image quality in all regions of the digital image 400 that were subjected to binarization coupled with an undisturbed color photograph 402 in the region of the image not subjected to binarization.

In still more embodiments, it may be advantageous to perform optical character recognition (OCR) based at least in part on the classification and/or result of classification. Specifically, it may be advantageous to determine information about the location, format, and/or content of text depicted in objects belonging to a particular class, and modify predictions estimated by traditional OCR methods based on an expected text location, format and/or content. For example, in one embodiment where an OCR prediction estimates text in a region corresponding to a “date” field of a document reads “Jan, 14, 201l” the presently disclosed algorithms may determine the expected format for this text follows a format such as “[Abbreviated Month][.][##][,][####]” the algorithm may correct the erroneous OCR predictions, e.g. converting the comma after “Jan” into a period and/or converting the letter “l” at the end of 2011” into a numerical one character. Similarly, the presently disclosed algorithms may determine the expected format for the same text is instead “[##]/[##]/[####]” and convert “Jan” to “01” and convert each set of comma-space characters “,” into a slash “/” to correct the erroneous OCR predictions.

Of course, other methods of improving upon and/or correcting OCR predictions that would be appreciated by the skilled artisan upon reading these descriptions are also fully within the scope of the present disclosure.

While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of an embodiment of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. 

What is claimed is:
 1. A method, comprising: receiving a digital image captured by a mobile device; and using a processor of the mobile device: generating a first representation of the digital image, the first representation being characterized by a reduced resolution; generating a first feature vector based on the first representation; comparing the first feature vector to a plurality of reference feature matrices; classifying an object depicted in the digital image as a member of a particular object class based at least in part on the comparing; and binarizing the digital image based at least in part on one or more of the classifying and a result thereof; wherein the binarizing comprises: determining an object class color scheme; adjusting one or more binarization parameters based on the object class color scheme; and thresholding the digital image using the one or more adjusted binarization parameters.
 2. The method as recited in claim 1, wherein generating the first representation comprises: dividing the digital image into a plurality of sections; and determining, for each section, at least one characteristic value, each characteristic value corresponding to one or more features descriptive of the section.
 3. The method as recited in claim 1, further comprising defining at least one hyperplane between at least some of the reference feature matrices, each hyperplane defining a boundary between first objects corresponding to one of the reference feature matrices and second objects corresponding to another of the reference feature matrices.
 4. The method as recited in claim 1, wherein the first representation is a color image.
 5. The method as recited in claim 1, wherein one or more of the reference feature matrices comprises a plurality of feature vectors, and wherein each feature vector of the reference feature matrices corresponds to at least one characteristic of an object.
 6. The method as recited in claim 1, wherein the comparing comprises an N-dimensional comparison, and wherein N is greater than
 50. 7. The method as recited in claim 1, wherein the first feature vector is characterized by a feature vector length greater than
 500. 8. The method as recited in claim 1, further comprising: determining one or more object features of the object based at least in part on the particular object class.
 9. The method as recited in claim 1, wherein generating the first feature vector comprises determining a color profile of some or all of the object.
 10. The method as recited in claim 1, further comprising predicting an identity of text depicted on the object using optical character recognition (OCR), wherein the predicting is based at least in part on the particular object class.
 11. The method as recited in claim 10, further comprising modifying at least one identity predicted using OCR based on an expected format of text depicted on the object, wherein the expected format is determined based at least in part on the particular object class.
 12. The method as recited in claim 1, further comprising one or more of: detecting the object depicted in the digital image based at least in part on one or more of the classifying and a result thereof; cropping the digital image based at least in part on one or more of the classifying and the result thereof; rectangularizing the object depicted in the digital image based at least in part on one or more of the classifying and the result thereof.
 13. The method as recited in claim 1, wherein the binarizing comprises: determining an object class mask; applying the object class mask to the digital image; and thresholding a subregion of the digital image based on the object class mask.
 14. The method as recited in claim 13, wherein the binarizing further comprises: adjusting one or more binarization parameters based on the object class mask; and thresholding the digital image using the one or more adjusted binarization parameters.
 15. The method as recited in claim 1, further comprising: determining a geographical location associated with the mobile device, wherein the classifying is further based at least in part on the geographical location.
 16. The method as recited in claim 1, further comprising: outputting an indication of the particular object class to a display of the mobile device; and receiving user input via the display of the mobile device in response to outputting the indication, the user input comprising either a confirmation, a negation, or a modification of the particular object class.
 17. The method as recited in claim 1, further comprising: determining one or more object features of the object based at least in part on the particular object class; and detecting one or more additional objects belonging to the particular object class based on the determined object feature(s), wherein the one or more additional objects are depicted either in the digital image or another digital image received by the mobile device.
 18. A method, comprising: generating a first feature vector based on a digital image captured by a mobile device; comparing the first feature vector to a plurality of reference feature matrices; classifying an object depicted in the digital image as a member of a particular object class based at least in part on the comparing; and determining one or more object features of the object based at least in part on the particular object class; determining one or more object features of the object based at least in part on the particular object class; and detecting one or more additional objects belonging to the particular object class based on the determined object feature(s), wherein the one or more additional objects are depicted either in the digital image or another digital image received by the mobile device.
 19. The method as recited in claim 18, wherein the one or more object features comprise an object color scheme, and wherein the method comprises binarizing the digital image based at least in part on: determining the object color scheme; adjusting one or more binarization parameters based on the object color scheme; and thresholding the digital image using the one or more adjusted binarization parameters.
 20. The method as recited in claim 18, wherein the one or more object features comprise an object class mask, and wherein the method comprises binarizing the digital image based at least in part on: determining the object class mask; applying the object class mask to the digital image; and thresholding a subregion of the digital image based on the object class mask.
 21. The method as recited in claim 20, wherein the one or more object features further comprise an object color scheme, and wherein the binarizing comprises: determining the object color scheme; adjusting one or more binarization parameters based on the object color scheme; and thresholding the digital image using the one or more adjusted binarization parameters.
 22. A system, comprising: a processor; and logic in and/or executable by the processor to cause the processor to: generate a first representation of a digital image captured by a mobile device; generate a first feature vector based on the first representation; compare the first feature vector to a plurality of reference feature matrices; classify an object depicted in the digital image as a member of a particular object class based at least in part on the comparison; determine one or more object features of the object based at least in part on the particular object class; and detect one or more additional objects belonging to the particular object class based on the determined object feature(s), wherein the one or more additional objects are depicted either in the digital image or another digital image received by the mobile device.
 23. A computer program product comprising: a non-transitory computer readable storage medium having program code embodied therewith, the program code readable/executable by a processor to: generate a first representation of a digital image captured by a mobile device; generate a first feature vector based on the first representation; compare the first feature vector to a plurality of reference feature matrices; classify an object depicted in the digital image as a member of a particular object class based at least in part on the comparison; determine one or more object features of the object based at least in part on the particular object class; detect one or more additional objects belonging to the particular object class based on the determined object feature(s); and wherein the one or more additional objects are depicted either in the digital image or another digital image received by the mobile device. 